One thing is never rely on what the GOM says in ECO mode.
If you want get a true reflection of the miles you're going to get, put the car in Sport mode and the heating on full heat and take a note of the range on the GOM, this is nearer the true figure. Then put it back into whatever mode you want and set the heater to what's comfortable, bearing in mind the GOM is now over reading by whatever it says minus the previous figure and base your charging stops on that (with some room for non-working chargers).
Another thing is speed, the ZS has the aerodynamics of a brick, so the faster you go the more it's going to affect your range. Stick to 50-60 mph if you can.
I salute you for setting out on such a long journey in the first place, you're braver than me and I wish you luck with your new ownership.